Deterministic photon-emitter coupling in chiral photonic circuits (1406.4295v3)

Abstract: The ability to engineer photon emission and photon scattering is at the heart of modern photonics applications ranging from light harvesting, through novel compact light sources, to quantum-information processing based on single photons. Nanophotonic waveguides are particularly well suited for such applications since they confine photon propagation to a 1D geometry thereby increasing the interaction between light and matter. Adding chiral functionalities to nanophotonic waveguides lead to new opportunities enabling integrated and robust quantum-photonic devices or the observation of novel topological photonic states. In a regular waveguide, a quantum emitter radiates photons in either of two directions, and photon emission and absorption are reverse processes. This symmetry is violated in nanophotonic structures where a non-transversal local electric field implies that both photon emission and scattering may become directional. Here we experimentally demonstrate that the internal state of a quantum emitter determines the chirality of single-photon emission in a specially engineered photonic-crystal waveguide. Single-photon emission into the waveguide with a directionality of more than 90\% is observed under conditions where practically all emitted photons are coupled to the waveguide. Such deterministic and highly directional photon emission enables on-chip optical diodes, circulators operating at the single-photon level, and deterministic quantum gates. Based on our experimental demonstration, we propose an experimentally achievable and fully scalable deterministic photon-photon CNOT gate, which so far has been missing in photonic quantum-information processing where most gates are probabilistic.

• The paper presents a deterministic approach that achieves over 90% directional single-photon emission using chiral photonic-crystal waveguides integrated with quantum dots.
• It employs engineered glide-plane waveguides to control circularly polarized transitions, achieving a beta factor of approximately 98% in emission efficiency.
• The research underpins scalable quantum photonics by proposing a deterministic CNOT gate model, advancing on-chip quantum information processing capabilities.

Deterministic Photon-Emitter Coupling in Chiral Photonic Circuits: A Detailed Analysis

The paper "Deterministic photon-emitter coupling in chiral photonic circuits" presents an ambitious exploration into the domain of chiral photon-emitter interfaces within photonic-crystal waveguides. It addresses a crucial challenge in photonic quantum-information processing: the creation of deterministic and directional photon-emitter interactions necessary for efficient on-chip device functionality.

Key Concepts and Experimental Findings

The central theme of the paper is the manipulation of photon emission directionality through the internal quantum states of emitters, facilitated by engineered photonic-crystal waveguides with chiral properties. The authors detail an experimental setup where single quantum dots (QDs), which serve as quantum emitters, are integrated within these chiral waveguides. A significant result showcased in this paper is the achievement of greater than 90% directionality in single-photon emission, with over 98% of emitted photons effectively channeled into the guided mode of the waveguide.

The experimental procedure involves exploiting the inherent asymmetry in the specially designed glide-plane waveguides (GPWs) to control and direct photonic emission. This involves utilizing circularly polarized transition dipoles of QDs, achieved through a magnetic field, thus dictating the chiral behavior of the emitted photons.

Implications of the Research

This deterministic and chiral coupling approach has profound implications for quantum photonics. It opens the avenue for developing on-chip optical diodes and circulators operating at the single-photon level. Critically, the paper also proposes a feasible architecture for deterministic all-photonic Controlled NOT (CNOT) gates—a pivotal building block in quantum computing—leveraging this controlled directional photon emission. The potential applications are not limited to quantum computing but extend to scalable quantum-information processing systems that require high-efficiency photon interaction interfaces.

Technical Results and Theoretical Considerations

Implications extend into the theoretical landscape as well, suggesting new potential for exploring topological photonic states in a manner analogous to electronic quantum spin Hall systems. The seamless integration of chiral photonic architectures into existing devices could lead to more robust and efficient quantum networks.

Experimentally derived measurements such as the directionality factor (average at 90%) and $\beta$-factor ($\sim$ 98%) highlight the efficacy of this engineered waveguide approach. The researchers emphasize the scalability and robustness of their architecture, suggesting further engineering could push these metrics even closer to ideal parameters.

Future Directions

The paper tentatively proposes extensions of these principles to other quantum-emitter platforms like atomic systems in photonic crystals, NV centers in diamonds, and superconducting qubits. This could lead to new regimes of photon transport and scattering that enhance our understanding of strong photon-photon interactions and nonlinear photonic behaviors.

Additionally, the proposed deterministic CNOT gate model, targeting a 96% entanglement fidelity, represents a concrete step forward, suggesting that experimental implementation could soon be plausible, provided the alignment of technological capabilities such as low-loss optical interfaces and reconfigurable beam-splitter circuits.

In conclusion, this research marks a significant advancement in photonic quantum-information systems, delineating a clear path towards deterministic photon interactions with significant applications in quantum computing and beyond. The adoption of chiral photonic circuits could represent an instrumental evolution in the pursuit of scalable and integrable quantum technologies.